The hypothalamic supraoptic nucleus (SON) contains both vasopressin-secreting (AVP) and oxytocin-secreting (OT) magnocellular neurons which release their respective hormones from the posterior pituitary gland into the systemic circulation. A direct relationship has been demonstrated in earlier physiological studies between the excitability of SON neurons and hormone release from the neurohypophysis. Catecholamines have been shown to activate SON neurons, thereby increasing the action potential frequency to the neural lobe. The present study examined the ability of catecholamines to evoke release of vasopressin and/or oxytocin from the neural lobe of an intraarterially perfused preparation of rat hypothalamo-neurohypophysis. / Experiments were carried out on male Long-Evans rats. Drugs (noradrenaline, dopamine, D1 and D2 dopamine receptor agonists) were delivered both into the perfusion medium and directly over the SON. Fractions of effluent medium were collected from the area of the neurohypophysis and tested for hormone release using a selective radioimmunoassay. Noradrenaline (NA) in concentrations of 10$ sp{-5}$ to 10$ sp{-4}$ M stimulated AVP release from neural lobe. The $ alpha sb1$-adrenergic receptor antagonist, prazosin (50 nM in perfusion experiments; 1$ mu$M in local injection experiments) blocked the noradrenaline-stimulated release. Dopamine (10$ sp{-4}$ to 10$ sp{-3}$ M), D1 (SKF 38393, 0.5 mM) and D2 (QNP 0.5 mM) dopamine receptor agonists also increased the release of AVP. In the presence of prazosin, DA, QNP and SKF 38393 still evoked AVP release. Therefore, it is proposed that both noradrenaline and dopamine stimulate the release of AVP in this preparation; the responses to dopamine appear to be mediated by both D1 and D2 dopamine receptors, presumably located at the level of the cell somata/dendrites, possibly also on axon terminals in the neural lobe.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.56990 |
| Date | January 1992 |
| Creators | Huang, Chunwei |
| Contributors | Renaud, L. P. (advisor), Polosa, C. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Physiology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001319310, proquestno: AAIMM87733, Theses scanned by UMI/ProQuest. |
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